1. Field of the Invention
The invention is in the field of optical time domain reflectometry and in particular the use of optical time domain reflectometry for sensing and quantifying volatiles.
2. Description of the Prior Art
A major goal of analyte detection research is to develop inexpensive, fast, reliable, and sensitive detectors. Unfortunately, the technologies developed to date have only met some of these goals, and no single device has sufficiently attained a majority of them.
Classical detection methods such as liquid chromatography (LC), gas chromatography (GC), and supercritical fluid chromatography (SFC), in combination with mass spectrometry, are widely used and provide accurate identification of analytes and quantitative data. However, these techniques are time consuming, extremely expensive, require sample preconcentration, and are difficult or impossible to adapt to field use.
Biosensors (i.e., devices containing biological material linked to a transducing apparatus) have been developed to overcome some of the shortcomings of the classical analyte detection techniques. Many currently used biosensors are associated with transducer devices that use photometry, fluorimetry, and chemiluminescence; fiber optics and direct optical sensing (e.g., grating coupler); surface plasmon resonance; potentiometric and amperometric electrodes; field effect transistors; piezoelectric sensing; and surface acoustic wave. However, there are major drawbacks to these devices, including their dependence on a transducing device, which prevents miniaturization and requires a power source. These disadvantages make such devices too complex, expensive, or unmanageable for many routine analyte detection applications such as field work or home use. Additionally, many of these devices are limited by the lack of stability and availability of the biological materials (e.g., proteins, antibodies, cells, and organelles).
Immunoassay methods are also used for detecting certain types of analytes. In these methods, antibodies are developed to specifically bind to a target of interest (e.g., an analyte). By labeling the antibody (e.g., with dye or fluorescent or radioactive material), binding of the antibody to an analyte can be detected. However, immunoassay methods are limited in that they require production of antibodies against each analyte of interest. Antibodies cannot be generated against some types of analytes and their generation can be time consuming and expensive.
The art remains in need of analyte detectors that provide the specificity of biosensors but also provide the cost-efficiency, stability, accuracy, reliability, reproducibility, and robustness that is lacking from available technologies. In particular, development of devices that can be miniaturized with controlled shapes and that do not rely on an energy source would also be very beneficial, particularly for routine field work and home use.
The electronic nose is the current state-of-the art technology for gas-phase chemical sensing. It consists of an array of carbon-black polymer composite films that act as vapor sensing elements by exhibiting a resistance response to vapor. The response across the array can be analyzed using chemometric methods that yield diagnostic patterns, which allow classification and quantification of analytes in gas-phase mixtures.
What is needed is some kind of volatile detection means which overcomes each of the limitations of the prior art.